Helical spring for producing artificial reverberation

ABSTRACT

A system for producing artificial reverberation using unidimensional wave guides reflectively terminated at both ends incorporates a helical spring excited into torsional vibrations by an electro-mechanical drive transducer, and includes at least one pick-off transducer converting mechanical vibrations into electrical vibrations. The drive transducer is at one end of the spring and the distance between the drive transducer and the pick-off transducer most remote therefrom corresponds to a signal transit time of substantially 50 ms. The overall length of the spring is at least 4 to 5 times this distance, and corresponds to a signal transit time of at least 200 ms. The surface of the helical spring is partially or wholly formed irregularly, and the spring has individual turns which are irregularly deformed.

United States Patent [151 3,662,292 Fidi et al. 1 May 9, 1972 [54] HELICAL SPRING FOR PRODUCING 3,517,344 6/1970 Fidi ..333/30 ARTIFICIAL REVERBERATION 3,270,300 8/1966 Leer ..333/3o 3,159,713 12/1964 Laube, .11. ..333/3ox [72] Inventors: Werner Fidi, Baden Bei Wien; Bernhard A. Weingartner, Wien, both of Austria [73] Assignee: AKG Akustiche U. Kino-Gerate GmbH,

Wien, Austria [22] Filed: Aug. 10, 1970 [21] App]. No.: 62,441

[30] Foreign Application Priority Data Aug. 18, 1969 Austria ..A 7890/69 [52] U.S. CL. ..333/29, 333/30, 179/] .6 [51] Int. Cl. ..H03h 9/30 [58] Field ofSearch ..333/29, 30, 71; 179/1, 1.6

[56] References Cited UNITED STATES PATENTS 3,136,853 6/1964 Bissonette et al ..333/30 X 2,375,004 5/1945 Knowles l79/l.6 X

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney-Toren and McGeady [5 7] ABSTRACT A system for producing artificial reverberation using unidimensional wave guides reflectively terminated at both ends incorporates a helical spring excited into torsional vibrations by an electro-mechanical drive transducer, and includes at least one pick-off transducer converting mechanical vibrations into electrical vibrations. The drive transducer is at one end of the spring and the distance between the drive transducer and the pick-off transducer most remote therefrom corresponds to a signal transit time of substantially 50 ms. The overall length of the spring is at least 4 to 5 times this distance, and corresponds to a signal transit time of at least 200 ms. The surface of the helical spring is partially or wholly formed irregularly, and the spring has individual turns which are irregularly deformed.

10 Claims, 4 Drawing Figures T 200 ms T HELICAL SPRING FOR PRODUCING ARTIFICIAL REVERBERATION BACKGROUND OF THE INVENTION Basically, systems for producing artificial reverberation using uni-dimensional wave guides reflectively terminated at both ends are required to simulate natural reverberation as closely as possible. Thus, the following basic requirements must be fulfilled:

l. The pole/zero configuration in the frequency spectrum must have a very high density.

2. Any periodicity in the time spectrum and in the frequency spectrum must be avoided.

3. The reverberation time should diminish towards low frequencies as well as towards high frequencies.

4. The mean frequency response also should have a diminishing characteristic towards low frequencies as well as towards high frequencies.

The use of homogeneous, uni-dimensional wave guides with a sufficiently dense pole/zero configuration in the frequency spectrum results in substantial delay periods which, in turn, are the cause of echoes and flutter echoes. If the pole/zero configuration is not sufficiently dense, a metallic, hollow and unnatural sound will result. In both cases, both the time spectrum and the frequency spectrum are completely periodic.

According to the second requirement above, it is necessary, therefore, for the signal, which is to be reverberated, to be dispersively resolved in a random manner. A high grade artificial reverberation can be produced with uni-dimensional structures only by such resolution or disintegration along the spring under the conditions of a high pole/zero configuration density, the pole values being statistically different over the entire transmission range.

To destroy such periodicities, it has already been proposed that the surface of the helical spring be rendered irregular, for example, by means of etching, and for the individual turns of such a spring to be irregularly deformed. While it has been shown that the quality of the reverberation thus produced is sufficient for mixing with the direct signal, the reverberation cannot be used directly by itself. The reason for this is due to the fact that, in known reverberation apparatus, the signal is impressed at one end of the delay line and is picked off at the other end.

In order to satisfy, in such an arrangement, the demand for a high-density pole/zero configuration whose periodicity is substantially destroyed by additional measures, it will be necessary to tolerate a long initial delay period. In reverberation systems in which the signal is impressed on one end of the helical spring and picked off at the other end, this results in an interferring delay of the first echo, since mixing of the direct signal with the reverberated signal produces a time gap. For example, with a pole/zero configuration density of 2.5 Hz, the first echo enters only after 200 ms.

However, the technical literature discloses that the first echo should occur with a maximum delay of 50 ms, or better still, with a smaller delay of, for example, only 30 ms. It has been found advantageous if a plurality of echoes occurs within the aforementioned interval of approximately 50 ms. It is furthermore essential that the first echoes, which are to correspond to those due to the first wall or ceiling reflections in natural vibrations, be reproduced with the least possible distortion, that is to say, with the highest possible signal fideli- Accordingly, no statistical dispersions should be present during the aforementioned time interval of 50 ms. All the requirements taken together cannot be satisfied byknown reverberation apparatus.

SUMMARY OF THE INVENTION This invention relates to systems for producing artificial reverberation using uni-dimensional wave guides reflectively terminated at both ends, and, more particularly, to such a system avoiding the defects of prior art system.

The invention makes use of a helical spring excited into torsional vibrations by means of an electro-mechanical drive transducer, and of at least one pick-ofi transducer for converting the mechanical vibrations into electrical vibrations. In accordance with the invention, the drive transducer is disposed at one end of the spring, and the distance between the drive transducer and the pick-off system most remote therefrom corresponds to a signal transit time of preferably 50 ms, with the overall length of the helical-spring being from 4 to 5 times this distance but corresponding to a transit time of at least 200 ms. The surface of the helical spring is wholly or partially formed irregularly, where appropriate, or individual turns of the spring are irregularly deformed, or both expedients are adopted.

In one preferred embodiment of the invention, that section of the helical spring disposed between the driving transducer and the pick-off transducer or transducers is fonned from a wire having a smooth surface. The remaining part of the helical spring has a wholly or partially irregularly formed surface and, where appropriate, includes a plurality of irregularly deformed turns.

As will be shown later, it has been found particularly appropriate for at least one electro-mechanical transducer, disposed along the length of the helical spring, to be provided with an attenuating system.

The inventive concept on which these measures are based resides in that a helical spring, with a delay period of at least 200 ms, is provided with at least one drive transducer and one pick-ofi transducer spaced respectively by a distance corresponding to a maximum signal transit time of 50 ms, and for the substantially longer part of the spring, not provided with any pickoff transducer arrangement, to be provided with an irregularly formed surface to produce a plurality of frequencydependent, statistical reflections within this latter part of the spring.

The frequency-dependent statistical reflections in the longer part of the spring produce a continual decay of the signal recorded on the pick-off system. If the same spring were to be employed without the irregularly formed surface and the individual, irregularly deformed, turns, it would mean that, in the case of a spring of infinite length, there would be no echoes while, in a very long spring, there would be echoes which would, however, be individually audible.

An object of the invention is to provide an improved system for producing artificial reverberation using uni-dimensional wave guides reflectively terminatedat both ends.

Another object of the invention is to provide such a system incorporating a helical spring excited into torsional vibrations by an electro-mechanical drive transducer and having at least one pick-off transducer spaced from the drive transducer and converting mechanical vibrations into electrical vibrations.

A further object of the invention is to provide such a system in which the drive transducer is at or adjacent one end of the spring, and the distance between the drive transducer and the pick-off transducer most remote therefrom corresponding to a signal transit time of substantially 50 ms.

Another object of the invention is to provide such a system in which the overall length of the spring is at least 4 to 5 times this distance and corresponds to a signal transit time of at least 200 ms.

A further object of the invention is to provide such a system in which a substantially longer part of the spring, with which there are associated no pick-ofi transducers, has an irregularly formed surface to produce a plurality of frequency-dependent, statistical reflections therein.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing:

FIG. la is a diagrammatic illustration of one embodiment of the invention, including electro-mechanical transducers disposed along a helical spring;

FIG. 1b is a view, similar to FIG. I, of another embodiment of the invention;

FIG. 2 is a pulse diagram of the system with the spring not having an irregularly formed surface; and

FIG. 3 is a pulse diagram of the same system but with the spring having a treated or statistically irregularly formed surface.

DESCRIPTION OF Tl-IE PREFERRED EMBODIMENTS In the embodiment of the invention as shown in FIG. la, electro-mechanical transducers 1, 2 and 3 are operatively associated with a helical spring 4. Transducer 1 functions as an electro-mechanical drive transducer to impress, on helical spring 4, the signal to be reverberated in the form of torsional vibrations.

Transducer 3 is an electro-mechanical pick-off transducer and is disposed at a distance from transducer 1 corresponding to a transit time of approximately 50 ms. Transducer 2 constitutes a further pick-off transducer which may be disposed at a shorter distance from transducer 1, and corresponding to a transit time of at least 30 ms.

In the embodiment of the invention shown in FIG. 1b, it is possible to dispense with the second pick-off transducer by utilizing the reflection on the spring end nearest to the recording or drive transducer. The differences in the transmission characteristic of the two embodiments are small and are, in particular, rendered diffuse by the dispersive resolution of the recorded signal. The phenomena which take place within the first50 to 100 ms may be completely adapted to each other if the recording and pick-off transducers are appropriately arranged as shown in FIG. lb.

Helical spring 4 extends beyond pick-off transducer 3, and the extending section has a length, in accordance with the invention, corresponding to a signal transit time of at least 200 ms. The spring portion 5, adjoining the last pick-off transducer in the direction away from the drive transducer, has a surface which which is statistically variable over its entire length, while the portion 6 of spring 4 which is associated with the electro-mechanical transducer systems preferably is provided with a completely smooth surface.

For manufacturing reasons, it is often appropriate for the spring to be surface treated over its entire length. This procedure results in a certain loss of quality which may, however, be regarded, in some circumstances, as tolerable. Depending on where, and on the manner in which, the surface of the spring is formed, it is possible to produce more or less intensive changes of the tone quality. For example, in the embodiment of the invention illustrated in FIG. la, it is possible for the section of spring 4 between transducers 1 and 2 to be provided with a smooth surface, for the section of spring 4 between systems 2 and 3 to be provided with the surface having only slight irregularities, and for the long section of spring 4, adjoining transducer 3, to be provided with a surface having substantial changes. If the longer spring part 5 were to be constructed without surface treatment to have a delay period of 200 ms, it would result in a pulse diagram of the type illustrated in FIG. 2. In FIG. 2, it is possible to recognize clearly the periodicity which, as already mentioned, must be avoided at all costs.

By comparison, FIG. 3 shows the pulse diagram of the same spring if the surface thereof is provided with statistical irregularities. In order to provide a better example, sinusoidal pulses with a mean frequency of I000 Hz were used in place of needle pulses. It can be seen that practically no periodicity is present, thus permitting a diffuse resolution of the signal. The time intervals, which are clearly recognizable in FIG. 2, are properly filled, in the pulse diagram of the surface treated spring as shown in FIG. 3. Accordingly, the echoes occurring at signal transit times of more than 50 ms, in the invention arrangement, cannot be distinguished, but the condition according to which the first echo appears substantially unchanged with an interval of 30 to 50 ms has been satisfied.

In general, reverberation systems which, taking the form of transit time elements, employ some mechanical systems capable of vibrating, are subject to a rise of reverberation time towards the lower frequency. For example, a reverberation system of average dimensions, having a reverberation period of 2 seconds at a frequency of 3 kHz, will have a reverberation period of IO seconds at a frequency of I00 Hz. Such an effect is extremely undesirable and therefore must be compensated by suitable measures.

This may be done by the attachment of damping material to the electro-mechanical transducers, but this procedure is effective only at low frequencies. Assuming suitable damping, it is possible for the reverberation time to be influenced, if desired, even over the entire frequency range to be transmitted. Normally, damping of the electro-mechanical transducer systems will be performed as indicated in FIGS. la and 1b, because this method is the simplest. However, it is also possible for the spring itself to be damped, for example by disposing it in a damping material or in oil.

A reverberation system embodying the invention supplies an artificial reverberation which, in practice, cannot be distinguished from the natural reverberation.

The illustrated embodiments described herein are those in which the drive system is disposed at one end of the helical spring and the first pick-off system is disposed at a distance corresponding to a signal transit time of approximately 30 to 50 ms. However, the principles of the invention are not limited to such an arrangement, but also cover embodiments in which the drive system is disposed at a distance from the ends of the helical spring, and in which the first echo must arrive within the first 50 ms and which furthermore contain the other inventive features. Such a system results in a reduction of the technical effort while providing approximately the same quality.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is 1. In a system for producing artificial reverberation using uni-dimensional wave guides reflectively terminated at both ends, and of the type in which the wave guide comprises a helical spring excited into torsional vibrations in the audible sonic range by an electromechanical drive transducer and incorporating at least one pick-off transducer converting such torsional mechanical vibrations into electrical vibrations: the improvement comprising, in combination, said drive transducer being at least adjacent one end of said spring; the signal transit time between said drive transducer and the pick-off transducer most remote from said drive transducer, at frequencies in the audible sonic range, being substantially 50 ms; the overall length of said spring being at least 4 to 5 times the distance between said drive transducer and said pick-off transducer most remote from said drive transducer, and the overall signal transit time of said spring, at frequencies in the audible sonic range, being at least 200 ms.

2. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least a part of the surface of said helical spring is formed irregularly.

3. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which the entire surface of said helical spring is formed irregularly.

4. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which individual turns of said helical spring are deformed irregularly with respect to a normal circular configuration.

5. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least a part of the surface of said helical spring is formed irregularly, and in which individual turns of said helical spring are deformed irregularly with respect to a normal circular configuration.

6. In a system for producing artificial reverberation, the improvement claimed in claim 5, in which the surface of that portion of said helical spring disposed between said drive transducer and a pick-off transducer comprises a wire having a smooth surface; the surface of the remainder of said spring being formed irregularly.

7. In a system for producing artificial reverberation, the improvement claimed in claim 6, in which said remainder of said spring includes a plurality of turns which are deformed irregularly with respect to a normal circular configuration.

8. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least one of said pick-off transducers includes a damping means.

9. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which said drive transducer is disposed at one end of said helical spring; said pick-off transducers including a first transducer disposed at a distance, from said drive transducer, corresponding to a signal transit time of substantially 50 ms and a second transducer disposed at a distance, from said drive transducer, corresponding to a signal transit time of at least 30 ms.

10. In a system for producing artificial reverberation, the improvement claimed in claim I, in which said drive transducer is disposed in spaced relation to said one end of said spring; there being a single pick-off transducer disposed at a distance from said drive transducer; the signal transit time between said drive transducer and said single pick-off transducer, at frequencies in the audible sonic range, being substantially 50 ms.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,292 Dated May 9, 1972 lnv fl Werner Fidi et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [72] "Baden Bei Wie'n" should read Baden bei Wien "Bernhard A. Weingartner" should read Bernard Weingartner [73] "AKG Akustiche U. Kino Gerate GmbH" should read AKG Akustische u. Kino-Gerate, Gesellschaft m.b.H.

Signed and sealed this 1st day of May 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents I FORM PO- uscoMM-Dc scene-Pas UIS. GOVERNMENT PRINTING OFFICE i959 0-365-334, 

1. In a system for producing artificial reverberation using unidimensional wave guides reflectively terminated at both ends, and of the type in which the wave guide comprises a helical spring excited into torsional vibrations in the audible sonic range by an electromechanical drive transducer and incorporating at least one pick-off transducer converting such torsional mechanical vibrations into electrical vibrations: the improvement comprising, in combination, said drive transducer being at least adjacent one end of said spring; the signal transit time between said drive transducer and the pick-off transducer most remote from said drive transducer, at frequencies in the audible sonic range, being substantially 50 ms; the overall length of said spring being at least 4 to 5 times the distance between said drive transducer and said pick-off transducer most remote from said drive transducer, and the overall signal transit time of said spring, at frequencies in the audible sonic range, being at least 200 ms.
 2. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least a part of the surface of said helical spring is formed irregularly.
 3. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which the entire surface of said helical spring is formed irregularly.
 4. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which individual turns of said helical spring are deformed irregularly with respect to a normal circular configuration.
 5. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least a part of the surface of said helical spring is formed irregularly, and in which individual turns of said helical spring are deformed irregularly with respect to a normal circular configuration.
 6. In a system for producing artificial reverberation, the improvement claimed in claim 5, in which the surface of that portion of said helical spring disposed between said drive transducer and a pick-off transducer comprises a wire having a smooth surface; the surface of the remainder of said spring being formed irregularly.
 7. In a system for producing artificial reverberation, the improvement claimed in claim 6, in which said remainder of said spring includes a plurality of turns which are deformed irregularly with respect to a normal circular configuration.
 8. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which at least one of said pick-off transducers includes a damping means.
 9. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which said drive transducer is disposed at one end of said helical spring; said pick-off transducers including a first transducer disposed at a distance, from said drive transducer, corresponding to a signal transit time of substantially 50 ms and a second transducer disposed at a distance, from said drive transducer, corresponding to a signal transit time of at least 30 ms.
 10. In a system for producing artificial reverberation, the improvement claimed in claim 1, in which said drive transducer is disposed in spaced relation to said one end of said spring; there being a single pick-off transducer disposed at a distance from said drive transducer; the signal transit time between said drive transducer and said single pick-off transducer, at frequencies in the audible sonic range, being substantially 50 ms. 